12m Deep Engineered Platform in combination with Dynamic Compaction (DC-10T) & Soil Improvement / Modification (SIM - Lime & Cement)
PROJECT SUMMARY:
Works were between March 2016 and December 2017; Powerbetter Soil Solutions carried out the earthworks, Dynamic Compaction (DC-10T), and engineering of Soil Improvement/Modification (SIM - Lime & Cement) on a new industrial development project at Kingswood Lakes, Cannock. The site was a former open cast mine and had been backfilled over the years with predominantly cohesive materials, to depths >20m.
The works were carried out to re-engineer indigenous subsoils, to alleviate the import of granular fill materials and the export of excess subsoils, by conducting a combination of; earthworks (both 5m deep excavation and backfill to internal/external areas), the formation of a 5m high surcharge, the controlled application of 6-7m deep dynamic compaction (DC-10T) works, and by carrying out necessary soil improvement/modification (SIM), with hydraulic powder lime and/or cement. This provided an engineered solution to form the three platforms suitable to support building foundations and associated external pavement construction.
EARTHWORKS SUMMARY:
The works were carried out to excavate of indigenous subsoils within the building footprint plus a 5m curtilage, to a depth of 5m from the building formation level.
This reduced level dig facilitated the use of DC equipment to compact the underlying soils to a minimum depth of 6-7m below reduced level dig formation. The excavated material was formed into a surcharge stockpile on a second building footprint, up to a height no less than 5m. This material was sampled and tested to meet the consultant engineer’s requirements, and in preparation for replacement in the first building excavation, once the DC works were complete.
DYNAMIC COMPACTION (DC-10T) SUMMARY:
Once the building was excavated to reduced level dig formation (-5m), a suitable working platform of 6F2 aggregate was created to facilitate the DC rig. Dynamic compaction (DC-10T) was carried out using the principle of three-drop cycles; primary drop locations, secondary drop locations, and tamping drops.
This was carried out as a minimum across the whole area of two building footprints. DC works were monitored by carrying out SCTP testing both pre and post DC works and aim to achieve a minimum 15% improvement in the bearing of the underlying soils, to a depth of 6-7m.
RE-PLACEMENT EARTHWORKS SUMMARY:
Upon completion of the DC, and after proof rolling, the main re-placement works of excavated materials followed, in placed layers not exceeding 250mm, and monitored to achieve >98% compaction, <5% air voids, and to achieve a bearing pressure of 100kN/m2 with less than 3.25mm settlement. All the results met the consultant engineer’s requirements and exceeded his minimum criterion.
SOIL IMPROVEMENT/MODIFICATION (SIM) SUMMARY:
Soils improvement/modification (SIM - Lime & Cement) works took place on the as dug materials, only as and when required, when it is being replaced in the excavation works in the building. This was only carried out if the re-placed materials could not meet the specification requirements unaided. This only occurred due to inclement weather, when it was required to add the hydraulic powder to the materials in order to carry on meeting the specification and progress the works.
The improvement/modification (SIM) of subsoils at the formation level, both in the building and externally, was carried out by using a hydraulic binder additive of lime or cement, to re-engineer the physical properties of the subsoils, by providing throughout the material an insitu CBR of 15% and 95% Compaction.
